This invention relates to a process for preparing, in high yield, a sulfurized olefinic product for use in lubricating oil compositions having a low chlorine content, a sulfur content of from about 40 to about 50 weight percent and a viscosity at 100.degree. C. of less than about 20 cSt.
A number of methods for the preparation of sulfurized olefinic products that can be used as additives for lubricants are described in the prior art.
Myers, U.S. Pat. No. 3,471,404, describes a process for the preparation of stable non-corrosive organosulfur compounds which are substantially monomeric. The monomeric organosulfur compounds are prepared by reacting the adduct formed from the reaction between an olefin and sulfur monochloride with an alkali metal sulfide and free sulfur in the presence of an alcohol or an alcohol-water solvent under reflux conditions. Subsequently, the polysulfurized olefin is contacted with an inorganic base in a water solution to remove chlorine to less than about 0.5 weight percent.
Papay, et al., U.S. Pat. No. 4,204,969, describe a method for the preparation of olefin polysulfides comprising the steps of reacting sulfur monochloride with a C.sub.3 -C.sub.6 aliphatic mono-olefin in the presence of a promoter consisting of a lower alcohol (preferably isopropanol) in order to form an adduct. The adduct is then reacted with sulfur or sodium sulfide in a ratio of 0.1 to 0.4 gram-atom of sulfur per mole of sodium sulfide in an aqueous alcoholic medium at a temperature ranging from 50.degree. C. to the reflux temperature. The mixture is held at reflux for 2-8 hours to assure complete reaction. After the reflux period, the alcohol is distilled from the mixture and the product recovered by conventional methods.
In addition, Borne, et al., U.S. Pat. No. 4,645,610, disclose a method for the preparation of olefin polysulfides comprising contacting an addition product produced by the reaction of at least one aliphatic monoolefin containing 2 to 5 carbon atoms and sulfur monochloride or dichloride with a hydrocarbyl halide and at least one sulfur compound selected from sulfides, hydrosulfides and polysulfides of alkali metals, ammonium or alkaline-earth metals and usually elemental sulfur in an aqueous or aqueous alcoholic medium at certain reaction conditions so as to obtain products whose kinematic viscosity is not too high. When an alcoholic reaction medium is used, the preferred alcohol is isopropanol. If necessary, the product is treated with an inorganic base subsequent to the formation reaction. The product thus obtained has a viscosity of about 4 to 20 mm.sup.2 /s and a halogen content of less than 1 weight percent.
Zaweski, et al., U.S. Pat. No. 4,954,274, describe a process for obtaining sulfurized olefinic compounds which are soluble in both mineral and synthetic oils of lubrication viscosity. The first stage of the process is conducted by adding an olefin to sulfur monochloride in the presence of minor amounts of an active Lewis acid to form an adduct. The adduct from the first stage of the process is then reacted with sodium sulfide and sulfur in an aqueous alkanol reaction medium (preferably isopropanol) at a temperature of about 50.degree. C. up to reflux. After reaction of the adduct with sodium sulfide and sulfur, the product is recovered by conventional methods such as removing alkanol, water washing, vacuum drying and filtering.
DeGonia, et al., U.S. Pat. No. 4,966,720, relate to sulfurized olefins useful as EP additives in lubrication oils and to a two-stage process for their preparation. In the second stage of the process a sulfur monochloride/aliphatic monoolefin adduct is reacted in a basic, aqueous alcoholic solution containing sodium sulfide at a temperature of from about 50.degree. C. up to reflux to form the sulfurized olefin. When using the preferred alcohol, isopropanol either alone or mixed with other alkanols such as tertbutanol, and a reaction temperature of preferably 75.degree. to 85.degree. C., the resulting sulfurized polyalkylene product of DeGonia, et al., typically contains more than 5000 ppm chlorine.
British Patent 1,308,894 describes a process for producing organic sulfides of high sulfur content utilizing a catalytic quantity of a lower aliphatic alcohol to form a sulfo-halogenated organic intermediate, and thereafter sulfurizing and dehalogenating the intermediate in the presence of a substantial quantity of a lower aliphatic alcohol by treatment with an aqueous alkali metal monosulfide solutions. For chlorine contents of less than 4000 ppm, British Patent '894 notes that short reaction times are considered important in the production of low viscosity products.
While the foregoing methods provide sulfurized olefin products which are useful in lubricant mixtures, the chlorine content of the products of the foregoing processes is generally above about 1000 ppm and often above 5000 ppm. There remains a need for a sulfurized olefinic product having a substantially lower chlorine content yet containing the amount of sulfur desired and having acceptable copper corrosion and viscosity characteristics.